The present invention generally relates to a mobile telecommunication method and a mobile telecommunication system. In particular, the present invention concerns a personal communication system typically known as a portable telephone, capable of utilizing a public telephone network with employment of a personal radio station, in which at least subscriber line segments are formed in a radio signal form.
Nowadays, a mobile telephone system (cellular telephone) is utilized as a portable (pocket) telephone similar to a cordless telephone. This system has a problem in that as the number of subscribers is increased, it becomes a shortage of available electromagnetic waves. As one solution, the cells are made small to improve reuse rate of the electromagnetic waves. When the cells are made small, the switching operations from cells to cells should be frequently performed in the mobile telephone. In particular, when an automobile is driven along boundaries of the cells, proper telephone conversation could not be expected. Accordingly, there is a certain limitation to make the cells of the mobile telephone system small. As a consequence, there are independently available such a mobile telephone system having relatively large cells, and also such a cordless telephone system in which cell diameters are reduced up to approximately 100 meters, thereby increasing the frequency reusability.
However, although these systems are such telephone systems using radio signals, these telephone systems do not employ a common subscriber interface. Thus, users should possess (use) a terminal specific to the telephone system under use.
To solve the above-mentioned inconvenience, ITU-R (International Telcommunication Unit Radiocommunication Study Groups) has investigated such a system capable of utilizing any telephone system with employment of a single terminal.
That is, ITU-R has considered FPLMTS (Future Public Land Mobile Telecommunication System) corresponding to a radio interface. A concept of this FPLMTS system will be described with reference to a systematic diagram according to an embodiment of the present invention, as shown in FIG. 1.
In the drawing, reference numeral 1 indicates a portable telephone corresponding to a personal station (will be referred to as "PS" hereinafter). Reference numerals 20 to 25 (symbolized as "2") represent personal base station (will be referred to as "CS" hereinafter). Reference numerals 30 and 31 indicate mobile stations (will be referred to an "MS" hereinafter). Reference numeral 4 indicates a mobile base station (will be referred to as "BS" hereinafter). Reference numeral 5 shows a communication satellite. Reference numeral 6 denotes a mobile communication base station (will be referred to as "MES" hereinafter). Reference numeral 8A represents a wire line network involving a mobile communication switching (exchange) station (will be referred to as "MSC" hereinafter). Reference numeral 10 is a local switching (exchange) machine. Reference numeral 7 denotes a position register center. Reference numeral 8B is an existing network such as ISDN and PSTN.
Further, symbol R 2 indicates a radio interface between PS (personal station) 1 and CS (personal base station) 2, symbol R 1 shows a radio interface between MS (mobile station) 30 or 31 and BS (mobile base station) 4, and symbol R 3 denotes a radio interface between MES (mobile communication base station) 6 and the communication satellite 5.
As shown in this drawing, in the FPLMTS system, the radio interface for PS 1 and CS 2 is unified as R 1, so that various radio services such as mobile telephones, satellite telephones, and office cordless telephones are available by employing a single PS (personal station) 1.
It should be noted that in the FPLMTS system, a similar service is assumed when the radio interface R2 between PS 1 and CS 2 is the same as the radio interface R 1 between MS 3 and BS 4. However, as to the radio interface R 1 utilized in the mobile telephone, a radius of a cell in one BS 4 should be selected to be on the order of 0.5 to 20 km in order to avoid frequent switching operations of the cells. Then, if the radio interface R 1 is identical to the radio interface R2, then it may be assumed that a shortage of radio wave frequencies seriously occurs, because of the very wide cell radius of this BS 4. As to the personal base station CS 2, the cell radius of this CS 2 is selected to be approximately up to 100 m with respect to the radio interface R2 for the personal station PS 1, in which while a user probably, relatively stops or walks, he will use the portable telephone. As a consequence, it could be expected that the radio wave frequencies are effectively utilized. It should be understood that a cell is defined as a region or area covered by a single base station.
The FPLMTS system is described more in detail, in "Next Generation Portable Telephone System" (published by NIKKAN KOGYO Newspaper, supervised by the Ministry of Posts and Telecommunications, Mobile Communication Division).
As described above, in accordance with the FPLMTS system considered by CCIR, various services such as mobile telephones office cordless telephones, and portable telephones are available by way of a single personal station (PS) 1.
To this end, however, as illustrated in FIG. 8, in case that CS (personal base station) 24 on a moving object 100 corresponds to such CS located at the nearest position from PS 1A which is possessed by another subscriber outside this moving object, PS 1A requests CS 24 on the moving object to register its location. In this case, although the subscriber does not ride in the moving object, the location registration of this subscriber is carried out with respect to CS 24 on the moving object, and when the moving object is moved so that the distance between this moving object and the subscriber becomes longer, a telephone communication is interrupted. On the other hand, it is not always limited that PS 1B on the moving object utilizes PBS 4 via CS 2 on the same moving object. If PB 1B on the moving object utilizes CS 2 fixed on the ground, then the cell switching operations are very frequently performed in connection with movements of the moving object. Furthermore, if such an operating mode is allowed, then a large-scale control system would be required, resulting in practical problems.
In other words, to realize such a system that various services are available by employing a single terminal unit, like in the FPLMTS system, it is required to selectively provide the necessary service, depending upon user conditions of PS, especially such a condition as to whether or not the user is on a high-speed moving object.